Actual pressure above zero, which is the atmospheric pressure added to the gauge pressure. It is expressed as a unit of pressure such as lbs. per sq. in. absolute (psia).

ACCUMULATOR – STEAM

A pressure vessel containing water and/or steam, which is used to store the heat of steam for use at a late period and at some lower pressure.

ACIDITY

Represents the amount of free carbon dioxide, mineral acids and salts (especially sulphates of iron and aluminum) which hydrolyze to give hydrogen ions in water and is reported as milliequivalents per liter of acid, or ppm acidity as calcium carbonate, or pH the measure of hydrogen ions concentration.

AIR DEFICIENCY

Insufficient air, in an air-fuel mixture, to supply the oxygen required for complete oxidation of the fuel.

AIR-FUEL RATIO

The ratio of the weight, or volume, of air to fuel.

AIR VENT

A valved opening in the top of the highest drum of a boiler or pressure vessel for venting air.

AMBIENT AIR

The air that surrounds the equipment. The standard ambient air for performance calculations is air at 80 °F, 60% relative humidity, and a barometric pressure of 29.921 in. Hg, giving a specific humidity of 0.013 LB of water vapor per LB of dry air.

ATMOSPHERIC PRESSURE

The weight of a column of air, one square inch in cross section and extending from the earth to the upper level of the blanket of air surrounding the earth. This air exerts a pressure of 14.7 pounds per square inch at sea level, where water will boil at 212°F. High altitudes have lower atmospheric pressure with correspondingly lower boiling point temperatures.

Atmospheric pressure as determined by a barometer usually expressed in inches of mercury.

BLOWDOWN

Boiler water that is removed from the boiler in order to maintain the desired concentration levels of suspended and dissolved solids in the boiler and removal of sludge.

BLOWDOWN VALVE

Also referred to as a blowoff valve. A valve which permits a boiler control to be flushed out, and the function of same to be checked.

BLOW-OFF VALVE

A specially designed, manually operated, valve that connects to the boiler for the purpose of reducing the concentration of solids in the boiler or for draining purposes. (Often called bottom blowdown.)

BOILER

A closed vessel in which steam is generated, or in which water is heated by fire or electricity.

BOILER CROWN

The part of a boiler which forms the top of the furnace in a fire box boiler, or the equivalent surface in other types of boilers.

BOILER EFFICIENCY

The term Òboiler efficiency” is often substituted for combustion or thermal efficiency. True boiler efficiency is the measure of fuel-to-steam efficiency.

BOILER FEED PUMP

A pump that is governed by a control that monitors the actual boiler water level; and only adds water to the boiler when the boiler needs it. The pump controller is mounted on the boiler.

BOILER HEATING SURFACE

The area of the heat transmitting surfaces in contact with the water (or steam) in the boiler on one side and the fire or hot gases on the other.

BOILER HORSE POWER

The equivalent evaporation of 34.5 pounds of water per hour at 212°F to steam at 212°F. This is equal to a heat output of 33,475 BTU per hour, which is equal to approximately 140 sq. ft. of steam radiation (EDR).

BOILER RATING

The heating capacity of a boiler expressed in boiler horsepower, Btu/hour, or pounds of steam/hour.

BOILER WATER

A term construed to mean a representative sample of the circulating boiler water, after the generated steam has been separated and before the incoming feed water or added chemical becomes mixed with it so that its composition is affected.

BOILING OUT

The boiling of highly alkaline water in boiler pressure parts for the removal of oils, greases, etc.

BRITISH THERMAL UNIT (BTU)

The quantity of heat required to raise the temperature of 1 pound of water 1°F.

BURNER

A device for the introduction of fuel and air into a furnace at the desired velocities, turbulence and concentration.

BURNER WINDBOX

A plenum chamber around a burner that maintains an air pressure sufficient for proper distribution and discharge of secondary air.

BURNER WINDBOX PRESSURE

The air pressure maintained in the windbox or plenum chamber measured above atmospheric pressure.

The rapid chemical combination of oxygen with the combustible elements of a fuel resulting in the release of heat.

COMBUSTION AIR

Air used in the combustion process. Air contains oxygen which is required to combust fuel.

COMBUSTION CHAMBER

See Furnace.

COMBUSTION EFFICIENCY

The effectiveness of the burner to completely burn the fuel. A well designed burner will operate with as little as 10 to 20% excess air, while converting all combustibles in the fuel to useful energy.

CONDENSATE

In steam heating, the water formed by cooling steam as in a radiator. The capacity of traps, pumps, etc., is sometimes expressed in pounds of condensate they will handle per hour. One pound of condensate per hour is equal to approximately 4 sq. ft. of steam heating surface (240 BTU per hour per sq. ft.)

CONDENSATE PUMP

A pump that is controlled by a switch mounted on the condensate tank. It adds water to the boiler when the condensate tank becomes full, whether the boiler needs water or not.

CONDUCTIVITY

(1) A material property relating heat flux (heat transferred per unit area per unit time) to a temperature difference. In American units, it is typically defined as the amount of heat (Btu) transmitted in one hour through one square foot of material 1 inch thick, with a temperature difference of 1°F between the two surfaces of the material. (2) The property of a water sample to transmit electric current under a set of standard conditions. Usually expressed as microhms conductance.

CONTINUOUS BLOWDOWN

The uninterrupted removal of concentrated boiler water from a boiler to control total solids concentration in the remaining water.

Removal of air and gases from boiler feed water prior to its introduction to a boiler.

DEW POINT

The temperature at which condensation starts.

DISSOLVED SOLID

Those solids in water which are in solution.

DISTILLATION

Vaporization of a substance with subsequent recovery of the vapor by condensation. Often used in less precise sense to refer to vaporization of volatile constituents of a fuel without subsequent condensation.

DISTILLED WATER

Water produced by vaporization and condensation with a resulting higher purity.

DRAFT

The difference between atmospheric pressure and some lower pressure existing in the furnace stack or gas passages of a steam generating unit.

DRAFT DIFFERENTIAL

The difference in static pressure between two points in a system.

DRAFT GAUGE

A device for measuring draft, usually in inches of water.

DRY FIRE

Insufficient water in a boiler to carry off the heat of combustion. It causes dry fire which results in cracked cast iron sections, and melted fire tubes.

DRY SATURATED STEAM

Saturated steam containing no water in suspension.

DRY STEAM

Steam containing no moisture. Commercially dry steam containing not more than one half of one percent moisture.

Equivalent direct radiation is the rate of heat transfer from a radiator or convector. It is equivalent to the square feet of surface area necessary to transfer heat at the same rate at which it is produced by a generator. A single boiler horsepower equals 140 ft2 EDR.

EFFICIENCY

The ratio of output to input. See also Combustion, Fuel-to-Steam and Thermal Efficiency.

ENTRAINMENT

The conveying of particles of water or solids from the boiler water by the steam.

EVAPORATION

The change of state from a liquid to a vapor.

EVAPORATION RATE

The number of pounds of water that is evaporated in a unit of time.

EXCESS AIR

Air supplied for combustion in excess of that theoretically required for complete oxidation.

A thermometer scale at which the freezing point of water is 32°F and its boiling point is 212°F above zero. It is generally used in the United States for expressing temperature.

FEEDWATER

Water introduced into a boiler during operation. It includes make-up and return condensate.

FEEDWATER TREATMENT

The treatment of boiler feed water by the addition of chemicals to prevent the formation of scale or to eliminate other objectionable characteristics.

FIRE TUBE BOILER

This type of boiler has the water on the external side of the tube and the heat (fire) on the internal side of the tube.

FIRING RATE CONTROL

A pressure temperature or flow controller which controls the firing rate of a burner according to the deviation from pressure or temperature set point. The system may be arranged to operate the burner on-off, high-low or in proportion to load demand.

FLAME DETECTOR

A device which indicates if a fuel (liquid, gaseous, or pulverized) is burning, or if ignition has been lost. The indication may be transmitted to a signal or to a control system.

FLAME PROPAGATION RATE

Speed of travel of ignition through a combustible mixture.

FLAME SAFEGUARD

A control that sequences the burner through several stages of operation to provide proper air purge, ignition, normal operation, and shutdown for safe operation.

FLASH (STEAM)

The rapid passing into steam of water at a high temperature when the pressure it is under is reduced so that its temperature is above that of its boiling point for the reduced pressure. For example: if hot condensate is discharged by a trap into a low pressure return or into the atmosphere, a certain percentage of the water will be immediately transformed into steam. It is also called re-evaporation.

FLUE

A passage for products of combustion.

FLUE GAS

The gaseous product of combustion in the flue to the stack.

FM

Factory Mutual.

FOAMING

A condition that occurs when an organic substance, usually oil, is floating on the surface of the water in a boiler. When the boiler is fired, a layer of foam develops on the surface of the water. This generally is indicated in the gauge glass by large swings in water level.

FREEZE UP

This refers to a structure that has lost its heating system, and the water in the piping freezes.

FRICTION HEAD

The pressure expressed in lbs./sq.in. or feet of liquid needed to overcome the resistance to the flow in the pipe and fittings.

FUEL

A substance containing combustible used for generating heat.

FUEL-AIR MIXTURE

Mixture of fuel and air.

FUEL-AIR RATIO

The ratio of the weight, or volume, of fuel to air.

FURNACE

An enclosed space provided for the combustion of fuel.

FURNACE PRESSURE

Pressure occurring inside the combustion chamber; positive if greater than atmospheric, negative if less than atmospheric, and neutral if equal to atmospheric.

FURNACE VOLUME

The cubic contents of the furnace or combustion chamber.

FUSIBLE PLUG

A hollowed threaded plug having the hollowed portion filled with a low melting point material.

Fresh water added to the system, by various means, to replace normal and abnormal water losses.

MANUAL RESET

A control that has to have human input before returning to normal operation.

MAXIMUM ALLOWABLE WORKING PRESSURE

The maximum gauge pressure permissible in a completed boiler. The MAWP of the completed boiler shall be less than or equal to the lowest design pressure determined for any of its parts. This pressure is based upon either proof tests or calculations for every pressure part of the boiler using nominal thickness exclusive of allowances for corrosion and thickness required for loadings other than pressure. It is the basis for the pressure setting of the pressure relieving devices protecting the boiler.

MAXIMUM DIFFERENTIAL (MD)

A control with this designation has a greater spread between on/off cycles.

MICRON

One millionth of a meter, or 0.000039 in. or 1/25400 in. The diameter of dust particles is often expressed in microns.

MINIMUM SAFE WATER LEVEL

Also know as safe operating level. The minimum level of water in a boiler where the burner will still operate. Below this level, the burner should be off due to low water.

MOISTURE LOSS

The boiler flue gas loss representing the difference in the heat content of the moisture in the exit gases and that at the temperature of the ambient air.

A control to start and stop the burner – must be in addition to the high limit control.

OPERATING PRESSURE

The pressure at which a boiler is operated.

ORGANIC MATTER

Compounds containing carbon often derived from living organisms.

ORIFICE

(1) The opening from the whirling chamber of a mechanical atomizer or the mixing chamber of a steam atomizer through which the liquid fuel is discharged. (2) A calibrated opening in a plate, inserted in a gas stream for measure velocity of flow.

OVERFIRING

A situation where the burner does not turn off, for a number of reasons. The pressure of the system rises and the safety relief valve should open.

OVERPRESSURE

Minimum operating pressure of a hot water boiler sufficient to prevent the water from steaming.

OXIDATION

Chemical combination with oxygen.

OXIDIZING ATMOSPHERE

An atmosphere which tends to promote the oxidation of immersed materials.

A boiler supplied with all of its components – burner, controls and auxiliary equipment, designed as a single engineered package, and ready for on-site installation.

PACKAGED STEAM GENERATOR

See Packaged Boiler.

PARTICLE SIZE

A measure of dust size, expressed in microns or per cent passing through a standard mesh screen. PASS – A confined passageway, containing heating surface, through which a fluid flows in essentially one direction.

The hydrogen ion concentration of a water to denote Acidity or Alkalinity. A pH of 7 is neutral. A pH above 7 denotes alkalinity while one below 7 denotes acidity. This pH number is the negative exponent of 10 representing hydrogen ion concentration in grams per liter. For instance a pH of 7 represent 10-7 grams per liter.

PILOT

A flame which is utilized to ignite the fuel at the main burner or burners.

PILOT VALVE

A valve that uses a small valve to operate a large valve.

PITOT TUBE

An instrument which will register total pressure and static pressure in a gas stream, used to determine its velocity.

PITTING

A concentrated attack by oxygen or other corrosive chemicals in a boiler, producing a localized depression in the metal surface.

PORT

An opening through which fluid passes.

POST PURGE

A method of scavenging the furnace and boiler passes to remove all combustible gases after flame failure controls have sensed pilot and main burner shutdown and safety shut-off valves are closed.

ppm

Abbreviation for parts per million. Used in chemical determinations as one part per million parts by weight.

PRECIPITATE

To separate materials from a solution by the formation of insoluble matter by chemical reaction. The material which is removed.

PRECIPITATION

The removal of solid or liquid particles from a fluid.

PREHEATED AIR

Air at a temperature exceeding that of the ambient air. PRESSURE – Force per unit of area.

PRESSURE

Force per unit area such as pounds per square inch.

PRESSURE DROP

The difference in pressure between two points in a system, caused by resistance to flow.

PRESSURE REDUCING VALVE

A piece of equipment for changing the pressure of a gas or liquid from a higher pressure to a lower one.

PRESSURE VESSEL

A closed vessel or container designed to confine a fluid at a pressure above atmospheric.

PRIMARY AIR

Air introduced with the fuel at the burner.

PRIMING

When the steam leaving the boiler carries large amounts of water with it, this is called priming. Insufficient heat, water hammer, and a flooded boiler, if the system has an automatic water feeder are some of the symptoms. It is generally caused by a high water level in the boiler, and near boiler piping.

PROCESS STEAM

Steam used for industrial purposes other than for producing power.

PRODUCTS OF COMBUSTION

The gases, vapors, and solids resulting form the combustion of fuel.

PULSATION

Rapid fluctuations in pressure.

PURGE

To introduce air into the furnace and the boiler flue passages in such volume and manner as to completely replace the air or gas-air mixture contained therein.

A comprehensive term used in a boiler-unit heat balance to account for the conduction, radiation, and convection heat losses from the boiler to the ambient air.

RADIATOR

A heating unit located within the room to be heated and exposed to view. A radiator transfers heat by radiation to objects “it can see” and by conduction to the surrounding air which in turn is circulated by natural convection.

RATED CAPACITY

The manufacturer’s stated capacity rating for mechanical equipment; for instance, the maximum continuous capacity in pounds of steam per hour for which a boiler is designed.

RATE OF BLOWDOWN

A rate normally expressed as a percentage of the water fed.

RATING

See “Load.”

RAW WATER

Water supplied to the plant before any treatment.

REACTION

A chemical transformation or change brought about by the interaction of two substances.

REASSOCIATION

The recombination of the products of dissociation.

RECIRCULATION

The reintroduction of part of the flowing fluid to repeat the cycle of circulation.

REDUCING ATMOSPHERE

An atmosphere which tends to 1) promote the removal of oxygen from a chemical compound; 2) promote the reduction of immersed materials.

REDUCTION

Removal of oxygen from a chemical compound.

REFRACTORY

Brickwork or castable used in boilers to protect metal surfaces and for boiler baffles.

RELATIVE HUMIDITY

The ratio of the mass of water vapor present in a unit volume of gas to the maximum possible mass of water vapor in unit volume of the same gas at the same temperature and pressure.

RELIEF VALVE (Safety Relief Valve)

An automatic pressure relieving device actuated by the pressure upstream of the valve and characterized by opening pop action with further increase in lift with an increase in pressure over popping pressure.

RESIDUAL FUELS

Products remaining from crude petroleum by removal of some of the water and an appreciable percentage of the more volatile hydrocarbons.

RESIN

A bead-like material used in chemical exchange for softeners and dealkalizers.

RESISTANCE

Impediment to gas flow, such as pressure drop or draft loss through a dust collector. Usually measured in inches water column (“wc).

Air which contains the maximum amount of water vapor that it can hold at its temperature and pressure.

SATURATED STEAM

Steam at the temperature and pressure at which evaporation occurs.

SATURATED TEMPERATURE

The temperature at which evaporation occurs at a particular pressure.

SATURATED WATER

Water at its boiling point.

SCALE

A hard coating or layer of materials on surfaces of boiler pressure parts.

SECONDARY AIR

Air for combustion supplied to the furnace to supplement the primary air.

SECONDARY TREATMENT

Treatment of boiler feed water or internal treatment of boiler-water after primary treatment.

SEDIMENT

(1) Matter in water which can be removed from suspension by gravity or mechanical means. (2) A non-combustible solid matter which settles out at bottom of a liquid; a small percentage is present in residual fuel oils. SEGREGATION – The tendency of refuse of varying compositions to deposit selectively in difference parts of the unit. <